A variety of nucleic acid species are capable of modifying gene expression. These include antisense RNA, siRNA, microRNA, RNA and DNA aptamers, and decoy RNAs. Each of these nucleic acid species can inhibit target nucleic acid activity, including gene expression.
MicroRNAs (miRNAs) are a class of 18-24 nt non-coding RNAs (ncRNAs) that exist in a variety of organisms, including mammals, and are conserved in evolution. miRNAs are processed from hairpin precursors of 70 nt (pre-miRNA) which are derived from primary transcripts (pri-miRNA) through sequential cleavage by the RNAse III enzymes drosha and dicer. Many microRNAs can be encoded in intergenic regions, hosted within introns of pre-mRNAs or within ncRNA genes. Many miRNAs also tend to be clustered and transcribed as polycistrons and often have similar spatial temporal expression patterns. MiRNAs have been found to have roles in a variety of biological processes including developmental timing, differentiation, apoptosis, cell proliferation, organ development, and metabolism.
miRNAs are an abundant class of non-coding RNA ranging from 20 to 23 nucleotides of length that are post-transcriptional regulators of gene expression. miRNAs have been mainly associated with developmental processes in metazoa such as Caenorhabditis elegans or Drosophila melanogaster (Ambros, 2004 Nature 431:350-5). However, evidence also suggests a role for miRNAs in a wide range of functions in mammals, including insulin secretion, heart, skeletal muscle and brain development (Kloosterman, et al., 2006 Dev Cell 11:441-50, and Krutzfeldt, et al., 2006 Cell Metab 4:9-12). Furthermore, miRNAs have been implicated in diseases such as cancer (Esquela-Kerscher, et al., 2006 Nat Rev Cancer 6:259-69) and hepatitis C (Jopling, et al., 2005 Science 309:1577-81), which make them attractive new drug targets. In contrast to the widely used RNAi technology using small interfering RNA (siRNA) duplexes, strategies to inhibit miRNAs have been less well investigated. Reverse-complement 2′-O-methyl sugar modified RNA is frequently being used to block miRNA function in cell-based systems (Krutzfeldt, et al., 2006 Nat Genet 38:S14-9). The use of miRNA inhibitors, however, remains challenging. Thus, there is a long felt need in the art for efficient and directed means of inhibiting miRNA. The present invention satisfies this need.